Inaccurate and misleading valve sizing: a proposed standard for valve size nomenclature

The sizes with which manufacturers label valves are nonuniform and haphazard. This has led to confusion and inappropriate comparisons of hemodynamics between valves with the same labeled size. Hemodynamic performance of valves is primarily determined by the internal diameter (ID) of their orifice.

The purpose of this study was to determine the ID and external diameter of aortic valves used at our institution and compare the measurements to manufacturers' labeled sizes. We also evaluated valve size (ID, manufacturers' labeled size) in 527 patients undergoing isolated aortic valve replacement between 1990 and 1996.

We demonstrated that no two manufacturers' tissue or mechanical valves have the same ID or external diameter for a given labeled size. The labeled size of tissue valves was 1 to 4 mm larger than the measured ID. The labeled size of mechanical valves was 3 to 5 mm larger than the measured ID. The St. Jude HP mechanical valve has a greater ID than all other mechanical valves for each labeled size. Among 403 patients operated on for predominant aortic stenosis, those patients receiving the Toronto Stented Porcine Valve (n = 98) had a larger mean ID (22.3+/-1.9 mm) than 204 patients receiving stented tissue valves (ID = 20.9+/-1.9 mm) and the 101 patients receiving mechanical valves (ID = 19.3+/-1.9 mm, p < 0.0001). However, when the manufacturers' labeled size was used as a measure of the size, the results were greatly exaggerated in favor of the Toronto Stented Porcine Valve (ID = 26.3+/-1.9 mm) compared with stented tissue valves (ID = 23.1+/-2.1) or mechanical valves (ID = 23.6+/-1.9) (p < 0.0001).

Manufacturers' labeling of valves is nonuniform and may lead to erroneous comparisons and conclusions of hemodynamic differences between valves. We therefore recommend a standardized nomenclature for the size of all valves based on the ID measurement.